In situ characterization of hydrogen absorption in nanoporous palladium produced by dealloying

Abstract

SummaryPalladium is a frequently used model system for hydrogen storage. During the past few decades, particular interest was placed on the superior H-absorption properties of nanostructured Pd systems. In the present study nanoporous palladium (np-Pd) is produced by electrochemical dealloying, an electrochemical etching process that removes the less noble component from a master alloy. The volume and electrical resistance of np-Pd are investigated in situ upon electrochemical hydrogen loading and unloading. These properties clearly vary upon hydrogen ad- and absorption. During cyclic voltammetry in the hydrogen regime the electrical resistance changes reversibly by almost 10% upon absorbing approximately 5% H/Pd (atomic ratio). By suitable loading procedures, hydrogen concentrations up to almost 60% H/Pd were obtained, along with a sample thickness increase of about 5%. The observed reversible actuation clearly exceeds the values found in the literature, which is most likely due to the unique structure of np-Pd with an extraordinarily high surface-to-volume ratio.

Hydrogen-induced plasticity in nanoporous palladium

“…1) shows a reversible expansion upon hydrogen ad- and absorption below −0.6 V, while a quasi-reversible expansion, attributed to the formation of a palladium-oxide species on the surface, is observed at potentials higher than −0.4 V. The term quasi-reversible refers to the small offset accumulated after an oxide half-cycle, which can be attributed to weak anodic palladium (oxide) dissolution [29]. The length changes upon voltammetric cycling are in agreement with recent results for dealloyed nanoporous palladium from different base alloys [17–18]. The highly reversible strain response upon hydrogen sorption and desorption in the CV motivated a more detailed investigation in this potential regime.…”

“…Lately, dealloyed nanoporous palladium (npPd) structures [16] have received attention in the literature as electrochemical actuator materials [17–20]. Due to the ability of palladium to host hydrogen atoms in its crystal lattice, such actuators show exceptionally strong, reversible expansion.…”

Dealloying progress during nanoporous structure evolution analyzed by in situ resistometry

“…1 By this method bulk quantities of nanoporous (np) metals can be produced, which find application in different fields of science and technology, ranging from energy storage 2,3 and (electro-)catalysis [4][5][6][7][8] to sensing [9][10][11][12] and electrochemical property tuning. [13][14][15][16][17][18][19] Dealloying is known to occur in a variety of different alloy systems, ranging from simple solid solution binary alloys 1,20 to more complex systems such as intermetallic compounds 21,22 or ternary alloys. 23,24 By far the most intensively studied dealloyed material is nanoporous gold (np-Au), selectively etched from solid solution Ag-Au master alloys, 1 with typical pore sizes in the range of tens of nanometers.…”

Pd‐Ni/Cd loaded PPy/Ti composite electrode: Synthesis, characterization, and application for hydrogen storage

“…The process of hydrogen storage on the Pd-Ni/Cd/PPy/ Ti electrode likely includes the following steps: (1) the electrochemical reduction of hydrogen ions on metal particles and (2) the subsequent migration of H atoms to the PPy film and diffusion on the support. 35 The estimated value of H/Pd ratio is slightly higher than that reported in the literature; for example, the H/Pd ratio was 0.66 at a potential of −325 mV according to Adams et al, 36 n H/ Pd ≅ 0.68 to 0.69 according to Mattarozzi et al, 34 and n H/Pd ≅ 0.60 according to Steyskal et al 37 3.2 | Characterization of Pd-Ni/Cd/PPy/Ti electrodes Figure 5A) is not smooth with small and irregular spherical protuberances dispersed well on the surface of the Ti substrate, which increases the specific surface area compared with the Ti substrate. In addition, PPy comprises π-conjugated conducting polymers, which is beneficial for dispersing the metal particles and modifying the electronic nature of the electrode.…”

“…The process of hydrogen storage on the Pd‐Ni/Cd/PPy/Ti electrode likely includes the following steps: (1) the electrochemical reduction of hydrogen ions on metal particles and (2) the subsequent migration of H atoms to the PPy film and diffusion on the support . The estimated value of H/Pd ratio is slightly higher than that reported in the literature; for example, the H/Pd ratio was 0.66 at a potential of −325 mV according to Adams et al, n H/Pd ≅ 0.68 to 0.69 according to Mattarozzi et al, and n H/Pd ≅ 0.60 according to Steyskal et al…”